1. Field of the Invention
The present invention relates to a keypad assembly for a portable communication device
2. Description of the Related Art
Generally, “portable communication devices” mean devices by which wireless communication can be performed while roaming. The portable communication devices include a hand-held phone (HHP), a cordless telephone (CT-)2 cellular phone, a digital phone, a personal communications systems (PCS) phone, and a personal digital assistant (PDA). The portable communication devices are typically classified into a bar type, a flip type, a folder type, and a sliding type according to their shapes, and equipped with an antenna apparatus, a data input/output device, and a data transceiver. For the data input device, a keypad or touch pad screen allowing data input through a finger activation is generally used.
As shown in FIG. 1, a conventional keypad apparatus 1 includes a Printed Circuit Board (PCB) 2 where a plurality of dome switches 3 and a plurality of Light-Emitting Diodes (LEDs) 4 are provided, a waveguide sheet 5 on the dome switches 3 which includes a diffusion pattern for reflecting incoming light toward a keypad 7, a base rubber portion 6 on the waveguide sheet 5 which includes a printed surface 6a on a top surface of which numbers and characters are printed. On a bottom surface of the base rubber portion 6 are formed a plurality of pressurizing protrusions 6b. 
As shown above, in the conventional keypad apparatus, the waveguide sheet, the base rubber portion having the pressurizing protrusions, and the keypad are disposed on the dome switches, which are provided on the PCB. However, this arrangement increases the thickness of the keypad apparatus and thus hindering the slimness design efforts of a product. Moreover, the waveguide and the base rubber portion having the pressurizing protrusions are essentially required which in turn degrades a clicking sensation of the keypad apparatus due to large thicknesses.
Furthermore, the conventional keypad apparatus is structured such that the LEDs provided close to the keypad. As a result, the keypad portion adjacent to the LEDs is bright due to high brightness therein and the keypad portion distant form the LEDs is dark due to low brightness therein. In other words, light from the LEDs does not uniformly illuminate the entire surface of the keypad due to distance variation, thus the keypad portion distant from the LEDs is darker and visibility of the keypad is degraded.
To solve the problem, a keypad apparatus using an Electroluminescent (EL) sheet in place of the conventional LED has been developed.
As shown in FIG. 2, a keypad apparatus 10 using a conventional EL sheet 11 is disposed under the entire surface of a keypad 12 in the form of a film to illuminate numeric and character key buttons formed on the keypad 12.
The EL sheet 11 is structured such that a transparent conductive film, an Indium-Tin Oxide (ITO)-Poly Ethylene Terephthalate (PET) film, is formed by depositing ITO on a PET film, an EL layer is formed by depositing a luminescent layer, a dielectric layer, and a back electrode on the transparent conductive film, and the EL layer is encapsulated by a protective layer (not shown).
In the EL sheet 11, once power is applied to a front electrode and the back electrode connected to ITO, the luminescent layer is excited on the whole, thus a surface light source uniformly emits light.
However, the keypad apparatus including the conventional EL sheet needs separate parts for providing an electric signal to the EL sheet for self-light-emission, thereby increasing the manufacturing cost and assembly processes of a product.
Therefore, there is a need for an apparatus which substitutes for the EL sheet and the conventional base rubber portion where the printed surface and the pressurizing protrusions are formed to achieve the slimness of the keypad apparatus, reduce the manufacturing cost, improve the efficiency of assembly processes, and improve a clicking sensation, and brightness and uniformity of the keypad.